1. Field of the Invention
The present invention relates to a method of smelting Zn bearing materials from Zn smelting plants and other sources by the use of a blast furnace (=MF furnace) and separating and recovering volatile valuable metals like zinc, cadmium, etc. as well as non-volatile valuable metals like gold, silver, copper, etc., together with an apparatus for practicing said method. Particularly it relates to a method and an apparatus for smelting Zn bearing materials which comprises blowing air into a blast furnace having a V-shaped or inclined hearth through tuyeres disposed along said hearth.
2. Description of the Prior Art
The residues from zinc smelting plants are generally classified into two classes, namely, a residue arising from the pyrometallurgical smelting process, such as the horizontal retort distillation process, the vertical retort distillation process and electric thermal distillation process, and a zinc leaching residue, to wit, the so-called `red residue` arising from the hydrometallurgical smelting process. Further, as other residues containing zinc, there are various kinds of dusts, such as fumed dust from open hearth, the converters, rotary kilns, etc. employed for iron manufacturing, the dust arising from copper ore smelting, hydrolysis cake, etc. These zinc bearing materials contain valuable metals such as Zn, Fe, Pb, Cu, Cd, Ag, Au, etc. From the view point of the effective use of resources as well as the prevention of environmental pollution ascribable to heavy metals contained in accumulated stocks, development of an appropriate method of recovering valuable metals contained in these materials has been long hoped for. As methods of recovering valuable metals contained in these zinc bearing materials, there are known the Jarosite method, the sulfatizing roasting method, etc. for hydrometallurgical leaching residues and the like, and for the residues arising from the pyrometallurgical smelting process, there are known a method of treating it by adding a reducing agent and using a rotary kiln as well as a blast furnace, etc.
The present inventor has previously proposed in Japanese Patent Publication No. 6681/1971 a method of smelting complex ores by the use of a blast furnace, said method being characterized in that, at the time of treating a complex ore containing Cu, Pb, Zn and other valuable metals by the use of a blast furnace, the thickness of the layer of the material is reduced or the feed is subjected to pre-heating or coking beforehand, pre-heated or oxygen-rich air is blown in by way of the vicinity of the tap hole, the melt is continuously discharged without accumulating it on the hearth thereby to emit a part of the furnace gas through the tap hole, and the smelting zone is maintained at a temperature of more than 1,300.degree. C. sufficient for reducing a part of the iron contained in the ore to metallic iron. As the blast furnace for use in this method, he has proposed a blast furnace intended for collectively enhancing the volatilization efficiency of zinc and improving the yield of metallic lead, said furnace being characterized in that, the furnace is of an ample length and provided with a weir disposed in the center of the hearth and outside the reach of the air blown in through the tuyeres, different kinds of ores mixed at an appropriate ratio are to be fed by way of the two sides of the furnace, the melt that forms in the vicinity of tuyeres of both sides is discharged through the tap hole of the respective side of the furnace so as not to get mixed together, and in order to recover oxides containing lead, tin and cadmium as well as zinc oxide or metallic zinc of high purity through a single stage, at the time of pre-heating or coking the ore material, a part of the waste gas in the furnace is separately led to the outside of the furnace and brought in contact with said ore material whereby the pre-heating or coking of the ore material is performed by using the waste gas without causing a reduction of the temperature of the overhead portion of the furnace.
More recently, the present inventor has proposed in Japanese Patent Publication No. 37889/1973 a method of smelting which comprises briquetting powder zinc leaching residue by adding a reducing agent thereto, subjecting the resulting briquetted ore to coking treatment within a coking chamber communicating with a blast furnace, feeding the thus coked material to the blast furnace in the form of a thin layer of material, blowing pre-heated air into the furnace from the lower part thereof close to the hearth and blowing secondary air into the overhead clearance within the furnace, maintaining the temperature of the surface of the layer of material as well as the reaction zone within the furnace at a specified temperature by regulating the amount of supply of the briquetted ore as well as the combustion within said clearance, recovering volatile valuable metals by effecting oxidation and combustion within the clearance, and recovering the non-volatile valuable metals in the form of matte by constantly emitting a part of the air blown into the furnace through the tap hole.
However, these methods of smelting in the prior art have drawbacks attributable to the employment of a blast furnace having the datum line of the tuyeres disposed horizontally, such as follows:
1. There occurs a difference of smelting speed between the two side parts along the length of the furnace and the central part thereof, and particularly the smelting speed of said two side parts is apt to slow down.
2. In the case where the strength of the briquetted ore is insufficient or the feed of ore material is increased, there occurs the so-called `dead` phenomenon in which the blowing of air into the two side parts through the tuyeres becomes impossible.
3. There are instances wherein clogging occurs in the tuyeres located on the two side parts of the furnace.
4. As to the smelting efficiency, using a furnace having a length of 4.2 m and equipped with single-sided tuyeres, the efficiency attained thereby is no more than 80 t/day in terms of ore material disposed of per unit furnace, and yet, enlargement of the size of furnace, and particularly lengthwise extension thereof, is difficult.